1. Field of the Invention
The present invention relates to a method of partially painting an article, and more particularly to a masking method suitable for partial painting of a product molded of synthetic resin.
2. Description of Relevant Art
Partial painting is a process of painting a portion of the surface of an article, while leaving the remainder unpainted. The partial painting process is also used to paint an object in two-tone or more colors.
Because partial painting requires that an area to be painted and an area not to be painted should be demarcated clearly from each other, the area not to be painted is ordinarily covered with masking tape or a masking plate. Where a surface to be painted is of a complex shape, however, it has been tedious and time-consuming to seal the edge of the masked area.
There are growing demands for partial painting of complicated article surfaces because more and more products of complex shape to be painted are molded of synthetic resin as the molding process is advanced. Examples of such molded products include interior components, bumpers, and other parts of automobiles.
Japanese Laid-Open Patent Publication No. 57-35970 discloses a partial painting method for partially painting a workpiece molded of synthetic resin. The disclosed painting method includes the steps of coating the surface of the workpiece with a vinyl-base strippable paint, drying the coated surface, and cutting the coating or film with a knife or a heat cutter to remove a film portion corresponding to a surface area which is to be painted, thus completing the masking of the workpiece surface. However, because most synthetic resin materials are soft and will be softened when heat is applied, the molded workpiece tends to be damaged by the knife or the heat cutter when the strippable film is cut. Where the workpiece suffers a large cut, it is readily understandable how disadvantageous such a partial painting process is. Even if the damage is small, a gap is formed between the surface of the workpiece and the strippable film covering the area not to be painted. Paint applied after the masking process is apt to seep into the gap. As a result, the paint invades the area not to be painted, and the edge of the painted area becomes dull and in misalignment with the prescribed cutting line.
Furthermore, many molded workpieces or articles have three-dimensional curved surfaces, and for this reason it is quite difficult to cut off the masking film in exact alignment with a desired cutting line according to the aforesaid cutting process. Therefore, the painted coating of the workpiece is frequently required to be corrected after the painting process.